The present invention relates to a transmission controller of a V-belt type continuously variable automatic transmission.
Conventionally, a V-belt type continuously variable automatic transmission, wherein the transmission gear ratio of vehicles such as cars is continuously changed by regulating the groove widths of a pair of pulleys (a primary pulley on the drive side and a secondary pulley on the driven side) over which a V-belt is traversed. Conventionally, as disclosed in Japanese Laid-Open (Kokai) Patent Application (A) numbered Heisei 4-272569 (1992) titled “HYDRAULIC CONTROL DEVICE FOR CONTINUOUSLY VARIABLE TRANSMISSION.”
The groove widths of the primary pulley and the secondary pulley are designed to change in response to the supplied hydraulic pressure (a primary pressure and a secondary pressure) to the cylinder chambers (the primary cylinder chamber and the secondary cylinder chamber) provided in combination with each pulley. The primary pressure and the secondary pressure are controlled so as to be the target primary pressure and the target secondary pressure according to the operational status while using the line pressure generated by the hydraulic pump as the main pressure. In addition, although there is also provided a V-belt type continuously variable automatic transmission wherein the line pressure is used as the secondary pressure as it is, in order to simplify these specifications, it is assumed in the present invention that the secondary pressure is also generated using the line pressure as the main pressure similar to the case of the primary pressure.
Here, with the conventional transmission controller of a V-belt type continuously variable automatic transmission, the target primary pressure and the target secondary pressure are determined in response to the operational status at that time, based on the detected signals transmitted from the operational status detection means, such as sensors to detect the revolution speed of each pulley. Further, by finding the deviations between the values of the detected signals transmitted from the primary pressure sensor to detect the actual primary pressure (hereinafter referred to as “the actual primary pressure”) and the secondary pressure sensor to detect the actual secondary pressure (hereinafter referred to as “the actual secondary pressure”) at that time and the values of the target pressures (the target primary pressure and the target secondary pressure), the aforementioned actual pressures (the actual primary pressure and the secondary pressure) are feedback controlled to eliminate their deviations. For example, as disclosed in Japanese Laid-Open (Kokai) Patent Application (A) numbered 2001-34918 titled “HYDRAULIC CONTROL DEVICE OF CONTINUOUSLY VARIABLE TRANSMISSION.”
Here, if the primary pressure deviation or the secondary pressure deviation is too high, the groove widths of the pulleys become unsuitable during the period until the actual primary pressure is converged on the target primary pressure or the actual secondary pressure is converged on the target secondary pressure. For instance, when the groove widths of the pulleys are too wide, the pinching and gripping force of the V-belt is insufficient which causes the V-belt to slip. The resultant disadvantage is reduced durability of the V-belt.
Then, in the conventional transmission controller of the V-belt type continuously variable automatic transmission, if the primary pressure deviation or the secondary pressure deviation is higher than the predetermined threshold value, the system judges that there is a possibility whereby slipping may take place on the V-belt. The aforementioned “convergence” is designed to be expedited by adding a predetermined compensation quantity to the control value of the line pressure which is the main pressure of the primary pressure and the secondary pressure to control the primary pressure or the secondary pressure on an increment side higher than the normal value.